Rigid bodies of glass foam or foamed ceramic material are widely used in the form of blocks, bricks and the like for insulating and structural purposes because of the refractory character of the product, its low density, its comparative high strength, and its excellent thermal-insulation characteristics.
Such materials can be produced by cutting a strip or bar of glass foam or ceramic foam, into discrete blocks, the blocks being thermally treated.
It thus is of interest to produce a continuous strip of the foamed glass or ceramic, collectively referred to as foamed material, in an economical and convenient manner.
The problem is complicated by the fact that the foamed material is generally produced by combining with a glass or ceramic batch, usually in the form of a mixture of solids, one or more blowing or expanding agents which, as the mixture is heated to fusion, expands to provide pores, bubbles or interstices in the material.
The apparatus which can be used to produce such a foamed-material strip or block can include a tunnel-type furnace in which the glass or ceramic materials are heated to fusion and blown, a feeder for introducing the material at the beginning of a transport path through this furnace, i.e. at the upstream end thereof, a cooler at the downstream end and, if desired, means for separating the blocks from the strip.
The blocks themselves may be further cooled, tempered or the like.
In general, the ceramic or glass precursors, mixed with the blowing agent must be heated to a temperature of 800.degree. C. to 900.degree. C. to form the foamed strip which generally is in a plastic condition at such temperatures and must be cooled to rigidify it.
In a continuously operating apparatus for this purpose, it is convenient to be able to deposit the material to be foamed in successive molds disposed in end-to-end relationship and then foam the material at the indicated temperatures, whereupon the foamed glass or ceramic is cooled to a temperature of about 500.degree. C. prior to or upon severing into individual blocks or bricks. The latter are subsequently cooled further.
Various prior art systems have been proposed which utilize such techniques or somewhat different ones. For example, in German patent document No. 13 01 009, two pairs of metal belts, moving horizontally and vertically define the molds in a muffle furnace to permit the expansion of the material, the expanded product being carried through the furnace between two belts.
An important disadvantage of this system is that the belts rub against the walls of the furnace which thus constrain the belts and must be lubricated to restrict wear.
The precooled strip of the foamed material is severed into blocks by a flying saw displaced transversely across the path of the foamed strip.
Notwithstanding the lubrication which is carried out in such systems, wear is still a significant problem and because lubrication is required in hot zones of the furnace, frequently the lubrication fails. Steel belts may become unusable because of these problems in muffle furnaces.
In another system, the material is foamed in sheet metal molds pushed through a muffle furnace in end-to-end relationship, the individual molds being filled with the foamable material being positioned in the furnace.
At the discharge end, the molds are subjected to a preliminary cooling, lowered and returned to the feed end. Here again the continuous strip of the foamed material can be cut into blocks which can be further cooled.
In this construction, the pushing force is applied from mold to mold directly and the retarding force of friction acts in the opposite direction. Experience has shown that the molds tend to deform and that the deformed molds form an irregular but continuous strip.